Marine Applications of Clean Agents

Of all the perils at sea, one of the most dangerous is fire. Difficult to deal with and potentially deadly, a fire at sea leaves the crew and passengers caught between two unforgiving elements.

There’s no local fire department to call and it is up to the crew to find, control and extinguish the fire. In addition to the requirements associated with onshore fire protection systems, shipboard fire protection systems must be designed so that safe navigation can be maintained in the event the fire protection system is activated.

Due to its unique combination of properties, Halon 1301 (CF3Br) served for over 30 years as a near-ideal fire protection solution in numerous applications, e.g., the protection of engine compartments in both small and large watercraft. Halon 1301 is characterized by high fire suppression efficiency, low toxicity, low chemical reactivity, electrical non-conductivity, and long term storage stability. However, due to its implication in the destruction of stratospheric ozone, Halon 1301 production was halted on January 1, 1994. As a result, clean fire protection agents characterized by negligible environmental impact, such as FM-200 and Inergen – which retain the desirable properties of high efficiency, low toxicity, low chemical reactivity, electrical non-conductivity and high stability – have been developed to replace Halon 1301 in challenging applications such as the protection of marine vessels.

Marine Fire HazardsFire hazards on ships correspond to the three major occupancies common to all ships: (1) engine compartments and their related auxiliary equipment, (2) cargo holds or tanks, and (3) accommodation and service areas.

A key application of the clean agents in marine vessels is the protection of engine compartments. Pleasure craft and small commercial boats typically employ gasoline for propulsion engines and onboard generators. The primary fire hazard in the engine compartment of commercial marine vessels is the fuel oil employed to run engines or boilers, which is usually either marine diesel fuel or the heavy oil known as Bunker C. The majority of engine compartment fires are caused by broken fuel or lubrication oil lines spraying onto hot surfaces such as engine casings or exhaust manifolds. Engine compartment fires are also caused by short circuits or failures of electrical components or devices located in or adjacent to the engine room.

Engine compartment fires are Class B fires, and characterized by very rapid fire growth. This rapid fire growth results in the production of potentially lethal levels of heat and combustion products (e.g., CO and CO2) within a very short time period, and it is therefore critical that the fire protection system provide extinguishment in as short a time as possible. Clean agent systems provide both rapid detection and rapid extinguishment and are able to extinguish these rapidly growing Class B fires while they are still in their incipient stage, limiting the amount of heat and toxic combustion products produced, and ultimately limiting the amount of damage to the engine compartment and the associated repair costs.

In addition to providing rapid extinguishment with minimal cleanup requirements in the protection of engine compartments, HFC and inert gas based clean agents such as FM-200 and Inergen are suitable for the protection of the various flammable solvents encountered in onboard flammable storage and handling areas. Both agents are chemically unreactive and compatible with solvents. The marine environment is by nature characterized by high humidity conditions, and their lack of chemical reaction with water renders the HFC and inert gas clean agents appropriate for marine fire protection applications.

Marine Clean Agent RegulationsSOLAS 74 – the SOLAS (Safety of Life at Sea) Convention is regarded as the most important of all international treaties related to the safety of marine vessels. The first version of the SOLAS Convention was adopted in 1914 in response to the Titanic disaster, and the Convention in force today is referred to as SOLAS 74. Fire-related requirements for marine vessels are described in SOLAS Chapter II-2, Fire Protection, Fire Detection and Fire Extinction, which includes detailed fire safety provisions for all ships as well as specific measures for passenger ships, cargo ships and tankers. Fixed gas fire extinguishing system requirements are described in SOLAS Chapter II-2, Regulation 5.

IMO/MSC Circular 848 – the IMO/MSC/Circ.848, Revised Guidelines for the Approval of Equivalent Fixed Gas Fire-Extinguishing Systems, as Referred to in SOLAS 74, for Machinery Spaces and Cargo Pump Rooms, covers requirements for the design of fixed gas fire extinguishing systems on marine vessels, and includes required fire tests which must be passed in order to obtain IMO approval.

NVIC 6-72 – the Navigation and Vessel Inspection Circular NVIC 6-72 describes the basic design of marine suppression systems, including cylinder storage locations, system controls and instructions, and system design review. USCG approved methods for FM-200 systems are also detailed.

Due to its weight and space advantages compared to inert gas clean agents, FM-200 is by far the most widely employed clean agent in marine applications. Protection of identical spaces with inert gas agents requires over three times the total storage cylinder weight of an FM-200 system. In addition, protection of identical spaces with inert gas agents requires over three times the deck space for system cylinder storage compared to an FM-200 system.

The US Navy and the US Army employ both FM-200 systems and “hybrid” FM-200/water spray systems in various watercraft. These hybrid FM-200/water systems combine an FM-200 gaseous agent – for guaranteed fire extinguishment – with a low-technology water spray system operating off of a ship’s water main – to provide cooling and facilitate re-entry and ventilation. The key benefits of the system are a large reduction in combustion and decomposition products and the provision of cooling of the protected space. The US Army replaced Halon 1301 systems with hybrid FM-200/water spray systems in more than sixty of their watercraft engine compartments, including engine compartments up to 1700 m3 (60,035 ft3) in volume. A small selection of military marine vessels protected by FM-200 clean agent systems are shown in Table 2.

FM-200 systems are also employed in the protection of pleasure craft. Pre-engineered FM-200 systems are available for the protection of engine compartments ranging in size from 0.7 to 43 m3 (25 to 1500 ft3), for both diesel and gasoline powered vessels. These systems employ a design concentration of 8.7% v/v FM-200 and are available as automatic only units, and also as combination manual/automatic systems, equipped with an optional manual pull cable. Automatic systems are heat actuated, discharging at 79 oC (175 oF). Engineered FM-200 systems, capable of protecting volumes in excess of 43 m3 (1500 ft3), are also available.

Conclusion
Traditionally, fire protection systems for the offshore and marine vessel industries have used ozone depleting Halon or life threatening carbon dioxide. The successful use of clean agents in demanding marine applications fully demonstrates their ability to reduce industry dependence on ozone depleting Halons and improve life safety. Although typically used in land-based facilities for the protection of Class A hazards, gaseous clean fire protection agents have found numerous applications for the protection of Class B hazards, especially in the protection of marine vessels. The perils of fire at sea can be successfully and effectively controlled through the use of clean agent fire protection technologies.

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